Gears harness the power delivered from the mains supply or battery and enable it to be delivered across different ranges of speed and torque.

Each gear has a maximum rotation speed and torque. For example Cordless Screwdrivers with one gear have a maximum speed of maybe 230 rpm with 10 Nm of torque.

However a variable speed general purpose drill driver may have a maximum speed of 2,000 rpm with 80 Nm of torque.

Models with more than one gear allow different / greater ranges of speed to be selected, say 0-200 and 0-600 for Cordless Screwdrivers and 0-1,100 rpm / 0-60 Nm and 0-3,000 rpm / 0-150 Nm for Rotary Drills.

So for light driving / drilling 1 gear is perfectly acceptable, but 2 gears (and even 3 for professionals) provide more versatility in the number of applications that can be handled.

Torque Control

Once you have used the gear selector switch to choose the appropriate gear how do you control how tightly to squeeze the trigger to attain the correct amount of power without over drilling a hole, damaging a screw or work surface or even worse injuring yourself?

The answer is to set the correct level of torque on the torque ring (apart from Impact Drivers which do not have adjustable torque settings and work in a different way).

Finding this resistance level is down to trial and error to begin with and will depend on the gear setting you have chosen (assuming there is more than one gear), the screw or bit you are using and the material you are negotiating.

But the important thing is that when the torque level is reached the motor’s clutch will kick in and disengage the gear to stop the action (not dissimilar to depressing the clutch on your car when the engine is in gear). Often you will hear a click when this happens.

So with a bit of trial and error you should have no problem drilling holes cleanly or driving screws accurately.